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Author Topic: Dangerous AC situation in reception hall - PLEASE READ  (Read 184390 times)

Mike Sokol

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Re: freak accident? help!
« Reply #80 on: May 10, 2012, 03:04:45 PM »


Again, RPBG is the sort of thing that most people won't even detect, because most appliances are single-source and won't share a common safety ground with another appliance, and most small appliances now don't even require a safety ground since they have nonconductive shells.

But there is one really big danger from plugging appliance into hot-grounded outlet. ELECTROCUTION!!!  I was teaching a NoShockZone seminar last year at Ball State University, and one of the students in the class remarked that the outlet in her family basement was "messed up" and the refrigerator would shock you if you stood on the damp concrete floor and touched the door handle. The solution was that everybody in her family "knew" to jump in the air while opening the refrigerator door to avoid a shock!!!   When I told her about the potential lawsuit her family would face if a repairman or neighbor went to the basement and leaned on the fridge, she was unimpressed. She had been doing this for years and assumed it was no big deal. Of course, that's death by electrocution just waiting to happen, but consumers seem oblivious to just how easy it would be to die from that scenario.

BTW: A non-contact tester (like a VoltAlert) will also tell you if a chassis is electrically hot,  but may false trigger as hot on a double-insulated "ungrounded" appliance. In that case, the chassis is actually at 60 volts (half the line voltage) just due to capacitive coupling in the power supply, but there's less than 1 milliamps of current flow, so your body discharges the voltage to whatever is grounding you. Yeah, that makes me a little uneasy too....

This whole business of double-insulated, ungrounded guitar amps also makes me feel a little squeamish. I saw a modern Roland guitar amp at a church last summer that had a factory "ungrounded" plug, but the chassis was a full 120 volts, and they said a lead singer had picked up a guitar plugged into it a few weeks before and got a nasty shock from it when he also touched the mic. Of course, that will teach lead singers to keep their hands off the instruments (just kidding) but highlights the fact that double-insulated "ungrounded" appliances can, in fact, internally short their chassis to the line voltage. And, of course, your guitar strings are tied to that same chassis. I have a really terrifying demonstration of that particular situation.

Mike     
« Last Edit: May 10, 2012, 03:08:53 PM by Mike Sokol »
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John Roberts {JR}

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Re: freak accident? help!
« Reply #81 on: May 10, 2012, 04:16:20 PM »

A lot of very smart people have put much time and effort into human safety but it is hard to get much movement without dead bodies, and/or profit motive.

I've already suggested this, but IMO UL "should" expand ground bond current testing to include audio common connections even if not labelled as ground.

To extrapolate out, this means even XLR cable shields should pass ground bond testing, to fully protect the meat puppets.  It's is easy to see that will never happen, but we can ask.

I have seen houses with miswired outlets declared uninhabitable, until the killer outlets are corrected. But that only happens after a death. 

How do we inform DIY electricians?

I submit that new outlets when purchased need warnings and instructions, but this alone would not prevent idiots from putting themselves at risk.

No easy answer...

Keep tilting at those windmills... but look out you don't get a shock if the windmill is making electricity.

JR

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Re: freak accident? help!
« Reply #82 on: May 10, 2012, 04:37:55 PM »

A lot of very smart people have put much time and effort into human safety but it is hard to get much movement without dead bodies, and/or profit motive.

I've already suggested this, but IMO UL "should" expand ground bond current testing to include audio common connections even if not labelled as ground.

To extrapolate out, this means even XLR cable shields should pass ground bond testing, to fully protect the meat puppets.  It's is easy to see that will never happen, but we can ask.

I have seen houses with miswired outlets declared uninhabitable, until the killer outlets are corrected. But that only happens after a death. 

How do we inform DIY electricians?

I submit that new outlets when purchased need warnings and instructions, but this alone would not prevent idiots from putting themselves at risk.

No easy answer...

Keep tilting at those windmills... but look out you don't get a shock if the windmill is making electricity.

JR

And check that chassis is not a live wire!
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Mike Sokol

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Re: freak accident? help!
« Reply #83 on: May 10, 2012, 04:40:05 PM »

How do we inform DIY electricians?

I submit that new outlets when purchased need warnings and instructions, but this alone would not prevent idiots from putting themselves at risk.

Well, one way to do this is hit them at the point of sales. We already have proposals into Lowe's and Home Depot to produce a series of in-store videos and on-line articles about properly installing outlets and testing them for RPBG's. Amprobe and Fluke have been contacted about supporting that sort of training, both for consumers at big box stores as well as local electricians and inspectors. And of course, we're already pitching the idea of these training videos and articles to a variety of pro-sound manufacturers.

And as you've predicted, we've only gotten some lukewarm response so far. It seems that nobody want to talk about this until the body count piles up. But all is not lost.... your feedback on this forum is valuable in convincing magazines, websites, and manufacturers that it's an important topic that shouldn't be dismissed so lightly.

Plus I hope that everyone who reads this thread understands the importance of checking your outlet power BEFORE plugging in your expensive gear....

Mike
« Last Edit: May 10, 2012, 04:42:47 PM by Mike Sokol »
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Mike Sokol

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Re: freak accident? help!
« Reply #84 on: May 10, 2012, 04:44:47 PM »

And check that chassis is not a live wire!

Nils.... not to be critical about hair, but your avatar looks like it got a big shock....  ;)

Mike

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Re: freak accident? help!
« Reply #85 on: May 10, 2012, 04:46:22 PM »

I have seen houses with miswired outlets declared uninhabitable, until the killer outlets are corrected. But that only happens after a death.

The house I now own with my wife had an interesting issue in the laundry room. We had a brand new Kenmore washer and dryer set put in there. One day whilst doing laundry my wife was reaching into the dryer while resting her hand on the locking nub of the front loading washer right next to the dryer. She got a good jolt. I whipped out the DMM and check between the dryer drum and washer enclosure. a bit over 100V. I checked the outlet the dryer was plugged into, it had a hot neutral swap. Now even so, it should not have been an issue. For some reason, the drum of the dryer was tied to neutral instead of ground. The ground wiring on both receptacles was correct. AFAIK, any metal parts that a person could come into contact with should only be tied to ground. I replaced both outlets with GFCIs when correcting the wiring issue and sent a message to Sears that I believe they might have a design or assembly issue. They didn't seem very concerned, which of course concerned me since it's a potentially fatal issue. Not good policy.
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Cameron Pro Audio

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Re: freak accident? help!
« Reply #86 on: May 10, 2012, 04:56:46 PM »

Nils.... not to be critical about hair, but your avatar looks like it got a big shock....  ;)

Mike

Why do you think I'm following this thread?
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Mike Sokol

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Re: freak accident? help!
« Reply #87 on: May 10, 2012, 04:58:57 PM »

The house I now own with my wife had an interesting issue in the laundry room. We had a brand new Kenmore washer and dryer set put in there. One day whilst doing laundry my wife was reaching into the dryer while resting her hand on the locking nub of the front loading washer right next to the dryer. She got a good jolt. I whipped out the DMM and check between the dryer drum and washer enclosure. a bit over 100V. I checked the outlet the dryer was plugged into, it had a hot neutral swap. Now even so, it should not have been an issue. For some reason, the drum of the dryer was tied to neutral instead of ground. The ground wiring on both receptacles was correct. AFAIK, any metal parts that a person could come into contact with should only be tied to ground. I replaced both outlets with GFCIs when correcting the wiring issue and sent a message to Sears that I believe they might have a design or assembly issue. They didn't seem very concerned, which of course concerned me since it's a potentially fatal issue. Not good policy.

The proper way to test for this sort of situation is to use GLIT (Ground Loop Impedance Tester) with a kludge cable probe that let's you check the ground impedance of every part of the appliance. Perhaps something wasn't bonded properly inside the washer or dryer.

And yes, it would be nice if Sears was a little more concerned, but big companies generally don't admit to anything with potential liability.

Mike

Paul Dershem

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Re: freak accident? help!
« Reply #88 on: May 10, 2012, 09:03:43 PM »

Well, one way to do this is hit them at the point of sales. We already have proposals into Lowe's and Home Depot to produce a series of in-store videos and on-line articles about properly installing outlets and testing them for RPBG's. Amprobe and Fluke have been contacted about supporting that sort of training, both for consumers at big box stores as well as local electricians and inspectors. And of course, we're already pitching the idea of these training videos and articles to a variety of pro-sound manufacturers.

And as you've predicted, we've only gotten some lukewarm response so far. It seems that nobody want to talk about this until the body count piles up. But all is not lost.... your feedback on this forum is valuable in convincing magazines, websites, and manufacturers that it's an important topic that shouldn't be dismissed so lightly.

Plus I hope that everyone who reads this thread understands the importance of checking your outlet power BEFORE plugging in your expensive gear....

Mike

My VoltAlert arrived today, and I want to thank you for your guidance.

If you REALLY want to get the word out, you may want to contact Tom Silva, of television's This Old House, or Mike Holmes, of Holmes on Homes and Holmes Inspection. Both of these guys are considered highly credible and enjoy an ardent following.
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Tim Perry

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Re: freak accident? help!
« Reply #89 on: May 11, 2012, 12:33:47 AM »


No easy answer...

Keep tilting at those windmills... but look out you don't get a shock if the windmill is making electricity.

JR

i was at a recording gig last year and raised a fuss about the band with a ratty PA who INSISTED on using a ground lift adapter on the while PA.  Tempers flared, I threatened to leave, an accommodation was reached.

I recorded by all separate mics (no splits from their mics). I later provided system for the band. 

Point is, no ground is a much more common occurrence then a hot ground pin. And arguing with someone who is certain that the way hes been doing it for years is just fine is nearly futile.
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Re: freak accident? help!
« Reply #89 on: May 11, 2012, 12:33:47 AM »


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